it would be unfair for one party to have power over others and be able to sue them to enforce his own rights when the 3rd party wanted to be no part of the contract
Wouldve been unfair in Dunlop v Selfridge
But
if it seems unfair on the party trying to enforce their rights, surely such a remedy will be available in Tort law
Contracts (Rights of Third Parties) Act 1999
it actually did little reform the law as it merely gave statutory authority to what was being done at common law already
the act may not be any more effective as there are ways of avoiding having effect- for example specifically excluding certain parties when that may be unfair which is possible with a carefully worded contract
But
there are advantages as it may provide greater protection whereas the common law was a little vague
has been successful in remedying problems in cases like Tweedle v Atkinson, where the husband was denied a claim because his name did not appear in the contract, the act would now allow a claim if it appears to "confer a benefit on him"